Transformer-winding.



F. F. BRAND.

TRANSFORMER WINDING.

APPLICATION FILED SEPT. 28| 1916.

1,242,649. Patented 00$. 9,1917.

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lnvntor Frederick F. Brand,

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windings having each two taps.

UNITED- STATES PATENT OFFICE.

FREDERICK 1'. BRAND, OI! PITTSFIELD, MASSACHUSETTS, ASSIG'NOR '10 GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

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To all whom it may concern:

Be it known that I, FREDERICK F BRAND, a subject, of theKing of Great Br1ta1n, residing at Pittsfield, county of Berkshire, State of Massachusetts, have invented certain new and useful Improvements in Transformer-Windings, of which the following is a specification.

My invention relates to electrlcal apparatus comprising a winding of a plurality of conductors parallelly connected near their ends, and especially where such conductors are'arranged to divide the total current in certain proportions between themselves as where the conductors are transposed at intervals for that purpose. My invention particularly relates to transform ers. objectof my invention is to provide intermediate taps for such windings wlthout too appreciably increasing the exchange current between the conductors, as for example without effectively nullifying the transposition of the conductors. Other objects will appear later.

In practically no case in heavy current a number of conductors in parallel, does the current divide equally between all of the conductors unless the conductors are especially arranged to accomplish this result. These differences in the current values are due to differences in the reactances or resistances of the conductors, or both. It is common, therefore, to transpose the conductors of such windings at certain intervals in order to balance up as much as possible the resistances and reactances of the individual strands. ()bviously where simple taps, such as are commonly employed, are brought out of a winding of parallel conductors, each tap ,comprlsing in efiect a single conductor electrically connected to all the conductors of the winding, those winding conductors are electrically. connected at and by each tap, and the efiect of any transposition of the conductors is more or less nullified unless the transposition is made in such a way as to completely balance the currents between Completely balancing the resistances and reactances of the conductors and hence the currents between every two taps, is an oppressive limitation on the design and construction of most apparatus, almost always in fact a condition which it is impossible to meet.

Specification 01 Letters Patent.

tap may be connected and Patented Oct. 9, 1917.

Application filed September 2a, 1916. Serial no. 122,741.

By my invention, however, substantially no such limitation is imposed by the taps. In common practice the terminals of the taps are generally located at some distance from where the taps leave the windings; uite frequently the terminals of transormer taps for example, are located near the tops or the bottoms of the transformer casings, the tap conductors extending from these positions to the windings. In the preferred embodiment of my invention the taps comprise each a plurality of conductors or conducting sections, one conductor or conductor section for each conductor of the winding to be reached by the tap, these sections or tap conductors being insulated from each other except adjacent the terminal. Adjacent the terminal they are preferably brought together in order that the disconnected as a unit. Any current exchanged between conductors of a winding through such a tap must twice traverse substantially. the full length of the tap, and the impedence of the circuit of the tap from the winding to the terminal and back is or may readily be made sufficient to minimize the exchange current to immaterial values. My invention is embodied then by providing the taps with sufiicient resistance to the passage of current between the conductors connected thereby to minimize the exchange currents between these conductors, preferably by providing the taps with a conducting section for each conductor of the winding, the sections of each tap being insulated from each other for a considerable distance from the connection points. In transformers as they are commonly constructed it will generally be found suificient to sectionalize the taps from the windings to the tap terminals where these are usually located.

In the accompanying drawings I have I illustrated a preferred form of my invention.

Figure 1 illustrates in elevation and somewhat diagrammatically a three-phase high rounded by a low voltage winding and a high voltage winding interleaved therewith. The windings on the three legs are substantially alike and hence only those on one leg need be described in detail. The high voltage winding comprises four groups of coils, 2, 3, 4 and 5. The low voltage winding comprises three groups of coils, 6, 7, and 8 interleaved therewith as illustrated. Certain connections of the high voltage windings are illustrated and other connections thereof are omitted, but the particular connections thereof are immaterial. Each group of low voltage coils really comprises a single helical winding,

the various coils gradually merging into each other as will be apparent from the drawing. One of the coils of the low voltage winding is illustrated in'plan in Fig. 2. It will be seen from this figure that the coil comprises but one turn only and is made up of three conductors, each of substantially a rectangular cross-section. These three conductors are sufficiently insulated from each other, except at their ends where they are connected together, to prevent the exchange of current. These conductors are especially arranged or transposed so as to divide the total current among them equally provided the total current traverses the full length of the winding; to accomplish this their relative positions are changed as they pass from one group of coils to the next. Thus in group 6 conductor 10 is the external conductor, conductor 12 is the internal conductor or the closest to the core, and conductor 11 is between 10 and 12. As the conductors pass from group 6 to group 7, however, they change their relative positions in such a way that in group 7 conductor 10 is the internal conductor, conductor 11 the external conductor, and conductor 12 the intermediate conductor. Likewise as the conductors pass from group 7 to group 8, they change their relative positions in such a way that in group 8 conductor 12 is the external conductor, conductor 11 the internal conductor, and conductor 10 the intermediate conductor. This transposition of conductors may be observed from Fig. 1; it is indicated diagrammatically in Fig. 3. Through the transposition of the conductors, each conductor occupies substantially the same position in the winding as every other conductor thereof (where the winding is considered as a unit from one end thereof to the other), and is of substantially the same reactance,

and the same length and hence resistance.

According to my invention, the taps provided for such a winding comprise each a number of conductors equal to the number of conductors of the winding; thus the tap 20 comprises three conductors insulated from each other except at the terminal 21 where they are connected together for convenience of attachment to an external circuit. This tap terminal 21, together with the other terminals is located 'near the base of the transformer. Each of the conductors of the tap 20 is attached to one of the conindicated. However, between the points 27 and 28, between 28 and 29, and between 27 and 29 (see Fig. 3) there exist differences of potential due to the fact that the conductors 10, 11 and 12, between these points and each of the ends of the winding, inclose different areas and are of different lengths and hence different resistances. Hence, were a simple, single-conductor tap brought out of the winding between the groups of coils 6 and 7, this conductor connecting together the winding conductors 10, 11, and 12 at the points 27, 28 and 29, an exchange current between the winding conductors 10, 11 and 12 would necessarily result. The same is true of any other group of adjacent points throughout the whole of the low voltage winding except at the ends thereof. Taps such as I have illustrated and described above however, comprising separate tap conductors for the different winding conductors, the tap conductors being connected together only at their terminals, ofier sufficient resistance to the passage of current to sufficiently minimize the exchanged current between the winding conductors to allow the use of such taps.

While I have described the principle of my invention and the best mode I have contemplated for applying this principle, other modifications will occur to those skilled in this art and I aim in the appended claims to cover all modifications which do not involve a departure from the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is

1. In electrical apparatus, a winding comprising a plurality of conductors connected in parallel, and a tap for said windin comprising a conducting section electrical y connected to each conductor, said conducting prising a plurality of conductors connected in parallel, and particularly arranged to divide the total current in certain proportions, and a tap for said winding comprising va conducting section electrically connected to each conductor, and a common terminal electrically connecting said conducting sections at some distance from such connection points, said sections being otherwise insulated from each other.

3. In electrical apparatus, a winding comprising a plurality of conductors connected in parallel, and a tap for said winding connected to the conductors thereof and ofiering material resistance to the passage of current between said conductors.

4. In a transformer, a high Voltage winding and a low voltage winding, said low voltage winding comprising a plurality of conductors connected in parallel and transposed at intervals to equalize their resistances and reactances, a tap for said low voltage winding comprising a conducting section electrically connected to each. conductor, and an accessible terminal for said tap, said conducting sections being con nected together adjacent said tap terminal but otherwise insulated from each other.

In witness whereof, I have hereunto set my hand this 23 day of $eptember, 1916.

FREDERICK F. BRAND. 

